Response of carbon sequestration in salt marshes to changes in nitrogen loading and sea level rise

Abstract:

Carbon uptake and storage in marine and terrestrial systems is a topic of considerable importance, given the current rate of increase in atmospheric carbon dioxide concentrations. This project investigates how sea level rise and nutrient enrichment impact salt marsh accretion in the Waquoit Bay Estuary on the southwest coast of Cape Cod, MA, USA. The region is a recognized hot spot of sea level rise over the past 25 years, and it has experienced accelerated nitrogen enrichment related to population growth over the past 60 years. Eleven piston cores were collected from four marshes experiencing a gradient in nutrient enrichment. Preliminary results are based on a 90 cm core from Sage Lot Pond that spans approximately 490 years. Sediment accretion rates, determined from ¹³⁷Cs and ²¹⁰Pb, indicate an acceleration in marsh vertical growth since 1950. Concurrent evaluation of bulk carbon content shows increased carbon burial over the same time period. Additionally, sediment nitrogen content has increased while δ¹⁵N values became heavier, potentially indicative of anthropogenic nitrogen loading. These data will contribute to our understanding of the capacity of the marshes to contribute to carbon burial while responding to changes in climate and land use.